The present invention relates to a radiography apparatus. Particularly, the present invention relates to a radiography apparatus for image-reconstructing a forward-path image and a backward-path image by performing a scan while moving a cradle on which a subject is laid in a forward direction, and performing a scan while moving the cradle in a backward direction opposite to the forward direction.
A radiography apparatus such as an X-ray CT (Computed Tomography) apparatus performs a scan for a region to be imaged in a subject by emitting radiation such as X-rays toward the region to be imaged and detecting radiation passing through the region to be imaged in the subject to acquire projection data for the region to be imaged. Based on the projection data obtained by performing the scan, a slice image in a slice plane through the region to be imaged is then image-reconstructed. Such a radiography apparatus is employed in a wide variety of applications including medical applications and industrial applications.
In performing such a scan, a scan is performed on a region to be imaged in the subject by a scan gantry in the X-ray CT apparatus moving an X-ray tube and a multi-row X-ray detector such that they rotate around a subject centering a direction of a body axis of the subject laid on a cradle. At that time, the X-ray tube emits toward the region to be imaged in the subject, for example, cone-shaped X-rays that radially extend in a channel direction, which lies along a direction of rotation around the subject, and in a row direction, which lies along an axis of the rotation. The multi-row X-ray detector in which a plurality of detector elements are arranged along the channel direction and row direction then detects X-rays passing through the region to be imaged in the subject to thereby generate projection data.
This scan is performed in a scan scheme such as an axial scan scheme, helical scan scheme or the like.
In addition, there has been proposed a shuttle scan scheme in which a scan is performed at a position upon which X-rays impinge while moving the cradle on which the subject is laid in a forward direction and while moving the cradle in a backward direction (for example, see Japanese Patent Application Laid Open No. 2002-65661, Japanese Patent Application Laid Open No. 2005-137389, and Japanese Patent Application Laid Open No. 2002-95655).
A scheme for performing a scan in the shuttle scan scheme in combination with the helical scan scheme is generally referred to as helical shuttle scan scheme. On the other hand, a scheme for performing a scan in the shuttle scan scheme in combination with the axial scan scheme is generally referred to as axial shuttle scan scheme.
Based on the projection data obtained by performing such a scan, a plurality of slice images are then image-reconstructed for a plurality of axial planes that are consecutively arranged in the direction of the body axis of the subject, for example. At that time, weighted addition processing is applied to projection data elements that face each other, and slice images each corresponding to an axial plane, which is a perpendicular plane having a perpendicular lying in the body axis direction, are image-reconstructed according to a Feldkamp-based image reconstructing technique, such as that generally referred to as a three-dimensional backprojection technique or a cone-beam backprojection technique, for example.